Current detection unit and relay terminal array

Abstract: A compact current detection unit which detects a failure in a relay terminal and provides a relay terminal array which has a failure detection function and is compact and easy to assemble The current detection unit includes two symmetrical bobbins; a core located within compartments of bobbins and has an air gap in it; holes in the bobbins which correspond to air gap in the core; coil wound on the compartments; and a circuit board fastened to the side of one of the bobbins on which a Hall element is mounted. A Hall element is inserted through and fixed in position by the holes in the bobbins and the air gap in the core. If a current is flowing through the coil, the lines of magnetic force generated in the core are detected by the Hall element located in the air gap. If no current is flowing, no lines of force are detected.

Description: Field of The Invention This invention relates to a current detection unit for a relay terminal array capable of detecting failures and containing a number of current detection units. Background of The Invention There are many types of relay terminals, including relay terminals which are not capable of transmission, relay terminals with transmitting capability, and I/O relay terminals with, for example, photocoupler input and transistor output. Since none of these existing relay terminals is capable of detecting relay failures (welding of contacts, faulty contacts, and so on) by themselves, faulty relays are slow to be detected. This delay leads to inconvenience, such as down time until a new relay can be installed. To detect a faulty relay, one could use a logic circuit which has as its inputs the presence or absence of a load current from the relay and an output signal from the relay coil. Based on these inputs, the circuit could judge whether there were a relay fault. With this proposed circuit however, certain problems can occur: (1) The range of load current which can be detected is limited; (2) There are limitations on the shape and dimensions of the current sensor; (3) It is difficult to provide adequate isolation between primary and secondary circuits and among the different poles; and (4) Such a device cannot be assembled efficiently. A current detection unit according to the preamble of claim 1 is known from GB-A-2 219 864. Summary of The Invention In light of the problems listed above, this invention has the advantage of providing a current detection unit which is compact and easy to assemble. The current detection unit of this invention is as defined in claim 1. The current detection unit operates as follows. When a current flows through the coil wound on the core compartment of the case, lines of magnetic force are generated in the core contained in the compartment. These lines of magnetic force are detected by the magnetic-to-electric converter element placed in the air gap in the core. The magnetic field which is detected is converted to an electrical signal and is output as a signal indicating the presence of a current. When there is no current flowing through the coil, no lines of magnetic force are generated in the core. The magnetic-to-electric converter element does not detect a magnetic field, so a signal indicating the absence of a current is output. This current detection unit has a core in a compartment provided in a case and a coil which is wound on that compartment. A circuit board which has a current detection circuit featuring a magnetic-to-electric converter element is mounted on one side of the case. The case is comprised of two halves which fit together symmetrically, so it can be assembled merely by joining the halves. If a relay remains on in the relay terminal array when it should be off, because of a failure such as contact welding or faulty contact, a current will continue to flow in the coil in the current detection unit, and the magnetic field generated in the core will be detected by the magnetic-to-electric converter element as described above. If a relay goes off due to a failure when it should be on, no current will flow in the coil, and the magnetic-to-electric converter element will not detect a magnetic field in the core. The output signal from the magnetic-to-electric converter element in these circumstances is used by a logic circuit to determine, based on this signal and the on/off state of the relay, that a relay has failed. This result is transmitted to external circuitry. The current detection unit of this invention achieves the following advantages: (1) The current flowing through a circuit flows through a coil so that it can be detected as a magnetic field by a magnetic-to-electric converter element. This scheme insures that the current in the coil will be detected reliably. When this detection device is built into a relay terminal array, failures of relays can be detected reliably by a logic circuit; (2) The spatial relationship between the magnetic-to-electric converter element and the core is firmly fixed during assembly; (3) Sufficient isolation is provided between the primary and secondary elements; (4) The device can be assembled efficiently. Since the case is composed of two symmetrical halves, it can be assembled merely by fitting two pieces together, a highly efficient mode of assembly; and (5) The configuration of this invention allows the unit to be assembled easily and enables it to be made more compact. Brief Description of The Drawings Fig. 1 is a partial exploded perspective view of the current detection unit of this invention; and Fig. 2 is a partial exploded perspective view of the current detection unit pictured in Fig. 1. Detailed Description Of The Invention An example of a current detection unit is shown in exterior oblique view in Fig. 1 and in partial exploded oblique view in Fig. 2 . Current detection unit 1 has two bobbins (half cases) 10, 20. Bobbins 10, 20 fit together symmetrically and contain core compartments 11, 21, respectively. Compartments 11, 21 form an annular chamber into which the core is inserted. The top halves of the compartments protrude from bobbins 10, 20. Annular core 30, which is contained in compartments 11, 21, has a partially isolating air gap 31 in it. The inner side of bobbin 10 has a snap fitting 12 and a boss 13 on it. Bobbin 20 has a depression 22 which corresponds to snap fitting 12 and a hole 23 into which boss 13 fits. Circuit board 40 is mounted to the outside of bobbin 10 by means of self-tapping screws 42 which are inserted through holes 43 in circuit board 40 and holes 14, 24 in bobbins 10, 20. A single Hall element 41 is mounted on the inside of circuit board 40, the side facing the bobbin. This is the magnetic-to-electric converter element which detects the magnetic field generated in core 30 and converts it to an electrical signal. Since circuit board 40 is mounted on the outer side of bobbin 10, Hall element 41 can pass through hole 15, through air gap 31 in core 30, and partially penetrate hole 25 in bobbin 20. This configuration allows Hall element 41 to detect with certainty the lines of magnetic force generated in core 30. On the front of circuit board 40 is the current detection circuit, which comprises various electronic components. In a relay terminal array, circuit board 40 is connected to another circuit board through connectors 45. Magnet wire 35 is wound a predetermined number of turns on compartments 11, 21 of bobbins 10, 20 to produce coil 36. In one aspect of the invention, coil 36 is wound starting from the top and ending at the top, so that both halves are wound in the same direction. In a current detection unit 1 configured in this way, core 30 is enclosed in compartments 11, 21 of bobbins 10, 20. When bobbins 10, 20 are joined, snap fitting 12 on bobbin 10 engages with depression 22 on bobbin 20 and boss 13 on bobbin 10 goes into hole 23 in bobbin 20. In this way bobbins 10, 20 are formed into an integral unit. Circuit board 40 is mounted on the side of bobbin 10. When coil 36 is wound and placed in compartments 11, 21, the assembly is complete. In the configuration described above, Hall element 41 is easily and reliably positioned in air gap 31 of core 30 at the time of assembly. This insures that the spatial relationship between Hall element 41 and core 30 will remain fixed. It also guarantees a sufficient isolation distance between the primary and secondary circuits and improves the efficiency of the entire assembly process. The operation of current detection unit 1 is described below. When a current flows through coil 36, lines of magnetic force are generated in core 30 inside compartments 11, 21. These lines of magnetic force are detected by Hall element 41 in air gap 31 and converted to an electrical signal. A signal indicating the presence of a current is output by the current detection circuit. When there is no current flowing through coil 36, no magnetic field is generated in core 30. Hall element 41 does not detect a magnetic field, and a signal indicating the absence of a current is output.

Claims: A current detection unit comprising: an annular core (30) having an air gap (31); a case (10, 20) having a compartment (11, 21) in which said annular core is disposed, and a hole (15) in said case disposed in a position corresponding to said air gap in said annular core; a circuit board (40) mounted on one side of said case, said circuit board having a magnetic-to-electric converter element disposed thereon, said magnetic-to-electric converter being inserted into said air gap of said annular core through said hole in said case; and a coil (36) wound on said annular core, characterized in that said case is comprised of two symmetrical halves (10, 20) adapted to be fitted together, each said half (10, 20) defining an annular compartment (11; 21), said annular compartments forming, as said compartment (11, 21), an annular chamber enclosing said core (30). A current detection unit as claimed in claim 1, wherein said case halves (10, 20) are identical.

Inventors: FUJIWARA TERUHIKO, FUJIWARA, TERUHIKO, FUJIWARA, TERUHIKO, C/O OMRON CORPORATION
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1994
Main classification: H01H47
IPC codes: H02B1, H01H50, H01H47, H01F38, G01R15